1. Field of the Invention
This invention relates generally to a method for detecting cooling fluid pump failure in a fuel cell system and, more particularly, to a method for detecting cooling fluid pump failure in a fuel cell system that includes measuring one or both of the temperature of the cooling fluid at the outlet from the fuel cell stack and the temperature of the cathode exhaust at the outlet from the fuel cell stack, and comparing the measured temperature to a temperature that would be expected based on the operating conditions of the fuel cell system to determine whether the cooling fluid is flowing through the stack.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. A hydrogen fuel cell is an electrochemical device that includes an anode and a cathode with an electrolyte therebetween. The anode receives hydrogen gas and the cathode receives oxygen or air. The hydrogen gas is dissociated in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The protons react with the oxygen and the electrons in the cathode to generate water. The electrons from the anode cannot pass through the electrolyte, and thus are directed through a load to perform work before being sent to the cathode. The work acts to operate the vehicle.
Proton exchange membrane fuel cells (PEMFC) are a popular fuel cell for vehicles. The PEMFC generally includes a solid polymer-electrolyte proton-conducting membrane, such as a perfluorosulfonic acid membrane. The anode and cathode typically include finely divided catalytic particles, usually platinum (Pt), supported on carbon particles and mixed with an ionomer. The catalytic mixture is deposited on opposing sides of the membrane. The combination of the anode catalytic mixture, the cathode catalytic mixture and the membrane define a membrane electrode assembly (MEA). MEAs are relatively expensive to manufacture and require certain conditions for effective operation.
Several fuel cells are typically combined in a fuel cell stack to generate the desired power. For the automotive fuel cell stack mentioned above, the stack may include about two hundred or more fuel cells. The fuel cell stack receives a cathode reactant gas, typically a flow of air forced through the stack by a compressor. Not all of the oxygen is consumed by the stack and some of the air is output as a cathode exhaust gas that may include water as a stack by-product. The fuel cell stack also receives an anode hydrogen reactant gas that flows into the anode side of the stack.
The fuel cell stack includes a series of flow field or bipolar plates positioned between the several MEAs in the stack. The bipolar plates include an anode side and a cathode side for adjacent fuel cells in the stack. Anode gas flow channels are provided on the anode side of the bipolar plates that allow the anode gas to flow to the anode side of the MEA. Cathode gas flow channels are provided on the cathode side of the bipolar plates that allow the cathode gas to flow to the cathode side of the MEA. The bipolar plates also include flow channels through which a cooling fluid flows.
The cooling fluid is pumped through the cooling fluid flow channels in the stack by a pump to maintain the stack at a desirable operating temperature, such as 60°-80° C., for efficient stack operations. However, if the cooling fluid pump fails, then the stack may overheat depending on the output load of the stack, possibly damaging the fuel cell components, such as the membranes. Therefore, it is necessary to monitor whether the cooling fluid pump is pumping the cooling fluid through the cooling fluid flow channels to prevent fuel cell stack failure.
One known technique for determining if the cooling fluid pump is operating is to provide a flow sensor at a suitable location in the cooling fluid flow line outside of the fuel cell stack to measure the flow rate of the cooling fluid. However, such flow sensors are typically expensive devices that add significant cost to the fuel cell system. It would be desirable to eliminate the flow sensor in the fuel cell system used for this purpose.